1. Field of the Invention
The present invention relates to a method and a device for single ended line testing for qualifying an electrically conducting line.
2. Description of the Related Art
Such a subject is already known in the art, e.g. from “TDR tutorial—Introduction to Time Domain Reflectrometry”. This document is published by the Granite Island Group in 2002 at the URL: http://www.tscm.com. There it is disclosed that a single ended line testing method, called Time Domain Reflectometry, is used for determining characteristics of a cable from measurements at one end of this cable. In this single ended line testing method, the Time Domain Reflectometry, further referred to as TDR, a pulse of energy is transmitted down the cable. When such a pulse reaches the end of the cable, or any discontinuity along the cable, part or all of the pulse energy is reflected back to the sending source. So at the same location where one injected the pulse, one can measure the reflected energy.
For Fault location based on this single ended line testing method such a single ended line testing system measures the time it takes for the signal to travel down the cable, see the problem, and reflect back. The single ended line testing system then converts this measured time to distance from this side of the cable and displays the information as a waveform and/or distance reading. Such a measurement is executed by using a plurality of excitation signals sent from the source towards the other end of the line.
Moreover from these reflected pulses, one can not only deduce the position of the discontinuity (based on the time delay of the reflected pulse), but furthermore other characteristics of the cable such as topology, cable losses and achievable bitrates with xDSL modems can be extracted taking into account all properties of the reflected pulse.
Since the reflected pulses are very small due to travelling twice the distance to the discontinuity (back and forth), these reflections are often obscured by (external) noise sources.
Averaging over different measurement results, using the same excitation signal, lowers the external random noise effects e.g. Xtalk, environmental noise. However, averaging will not reduce the non-linearities or other noise sources that are synchronous with the applied excitation signal. Since the non-linearities are a (complex) function of the applied excitation signal, these non-linearities will behave as deterministic noise. It is noise because these components are undesirable and it is deterministic because this noise component is related to the excitation signal. Hence, by averaging over different measurements one will not lower the undesirable effect of non-linearities.